1302. Deepest Leaves Sum

https://leetcode.com/problems/deepest-leaves-sum/

1. Use recursion:

//48 ms    28.7 MB
/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    int deepestLeavesSum(TreeNode* root) {
        if(!root) return 0;
        int result = 0;
        int max_depth = maxLeave(root, 0);
        deepestLeavesSum(root, 0, result, max_depth);
        return result;
    }
private:
    int maxLeave(TreeNode* root, int depth){
        if(!root) return depth - 1;
        int d_l = maxLeave(root->left, depth + 1);
        int d_r = maxLeave(root->right, depth + 1);
        return max(depth, max(d_l, d_r) );
    }
    void deepestLeavesSum(TreeNode* root, int depth, int& result, int max_depth) {
        if(!root) return;
        deepestLeavesSum(root->left, depth + 1, result, max_depth);
        deepestLeavesSum(root->right, depth + 1, result, max_depth);
        //cout << depth << " " << root->val << endl;
        //cout << max_depth << " " << (depth == max_depth) << endl;
        if(depth == max_depth){
            result += root->val;
            return;
        }
    }
};